VIBRATION OF DELAMINATED COMPOSITE PLATES AND SOME APPLICATIONS TO NONDESTRUCTIVE TESTING

The impact of delaminations on the natural frequencies of composite plates, as well as delamination dynamics over a broad frequency range, is studied using the finite element method based on the three-dimensional theory of linear elasticity. For the case of cantilever laminated plates, the method is successfully compared with experimental observations. The results for delaminated plates indicate that even for large flaw sizes, the first few natural frequencies are not significantly affected. For higher frequencies, an overall reduction whose magnitude increases with the size and number of delaminations is predicted. At very high frequencies, the delamination vibrates independently and out of phase with the rest of the structure. At a particular frequency region, local flaw vibration causes dissipation of mechanical energy into heat. By utilizing thermographic and thermoelastic non-destructive evaluation techniques, the fast and easy detection and evaluation of delaminations follows.